Given a list of source items, a target item of the same type as source items, and a
lambda expression that returns a double value (a score) from those items, this function
will return a double that is the percentile into which that target value falls for the
population represented by the list of source items.

Note1: Percentile is the percent of observed values in the srcItems that fall at
or below the value of the targetItem.

Note2: If this operation will be performed repeatedly on the same list, use the other form instead.